Graphene is a conductive material configured such that carbon atoms are arranged in two dimensions in a honeycomb shape that is as thin as a single atomic layer. It is formed into graphite when stacked in three dimensions, into carbon nanotubes when rolled up in one dimension, or into a fullerene ball shape when rolled up to have zero dimensions, and has become an important subject of thorough research to determine the wide variety of low-dimensional nanophenomena thereof.
As known in the art, graphene is very structurally and chemically stable and is a very good conductor because it is able to transport electrons 100 times faster than silicon and enables the flow of current about 100 times larger than copper. These characteristics of graphene, which were first predicted, have since been experimentally confirmed by discovering a method of separating graphene from graphite.
Graphene is composed exclusively of carbon, which is relatively lightweight, and is thus easily processed into a one-dimensional or two-dimensional nanopattern. Accordingly, semiconductor-conductor properties may be adjusted using graphene, and moreover, the fabrication of various functional devices, such as a sensor, a memory, etc., using graphene is possible by virtue of the flexibility of graphene.
Since mass synthesis methods have not been developed despite the excellent electrical, mechanical, and chemical properties of graphene, research into techniques for real-world applications thereof is somewhat limited.
The synthesis of graphene may include, for example, mechanical or chemical exfoliation, chemical vapor deposition, epitaxial synthesis, organic synthesis and the like. Among these, a chemical vapor deposition process is regarded as very suitable for mass production of graphene having high quality and a large area.
In conventional mass synthesis methods, graphite is mechanically ground, dispersed in a solution, and self-assembled to thus form a thin film. Such a mechanical grinding process enables the synthesis of graphene at relatively low cost, but is problematic because many graphene flakes are overlapped and interconnected, and thus the resulting electrical and mechanical properties do not meet expectations.
To date, the growth of graphene in the chemical vapor deposition process has depended on the surface morphology of a metal catalyst for the initial growth of graphene, that is, the surface roughness of a metal catalyst. When the surface of the metal catalyst is smooth, monolayer graphene may be easily grown, whereas when the surface thereof is rough, multilayer graphene may be grown.
In the case where a metal catalyst layer having an initially rough surface is used, even when the processing conditions for chemical vapor deposition are controlled, it is difficult to obtain monolayer graphene. Furthermore, the number of layers of graphene is dependent on the initial surface roughness of the metal catalyst layer, rather than the conditions for chemical vapor deposition, making it difficult to efficiently control the number of layers of graphene as needed.